I propose to develop, study and utilize systems in several types of cultured mammalian cells to determine the biochemical and genetic mechanisms involved in regulative amino acid biosynthetic pathways. The development of these systems will invovlve the isolation and characterization (biochemical and genetic) of both structural gene and regulatory gene mutants affecting the amino acid biosynthetic pathways for proline, glutamine, arginine and asparagine. A series of such mutants will enable me to examine the nature, function and genetic location of various regulatory loci affecting these pathways in animal cells. For each of the systems, I have developed selective procedures that will provide the required regulatory and structural gene mutants, some of which have already been isolated. The goal of this project is threefold: (1) to determine the biochemical patterns and genetic mechanisms involved in regulating the above-mentioned biosynthetic pathways, (2) to identify (through the study of appropriate mutant) specific regulatory loci affecting these pathways, and how mutations in them alter the normal regulatory loci, and mutations affecting them at a molecular level and determine whether various regulatory loci are genetically linked or unlinked to the structural genes whose expression they modify.